1. Field of Invention
This invention is directed to increasing the illumination density color within a field of view of an imaging system.
2. Description of Related Art
Uniform, diffuse illumination of a workpiece is often necessary in commercial vision systems to accentuate an edge of the workpiece within a designated field of view. Since most workpieces are not transparent, diffuse illumination of the workpiece is also necessary so that light which is reflected from the workpiece can be collected by an imaging system. Furthermore, an adjustable diffuse illumination source accommodates the observation and inspection of workpieces having a wide variety of shapes.
The adjustable illumination provides the ability to illuminate workpieces having different characteristics, such as, for example, shape, composition, and surface finish. In some systems, the intensity of light emitted by a light source is adjustable when the magnification of the imaging system is adjustable.
Also, conventional lighting systems project light onto the workpiece at an adjustable angle relative to an axis which is normal to the imaging plane. This angle is referred to as the angle of incidence. In many conventional vision systems, the axis normal to the imaging plane is parallel to, or coincides with, the optical axis of the vision system. Light projected at an angle of incidence which is between 0xc2x0 and 90xc2x0 may improve the surface contrast of the image and may also more clearly illuminate textured surfaces. Typically, such light sources have a prescribed range for the angle of incidence varying between 10xc2x0 and 70xc2x0. Such a range is relatively broad and, therefore, provides adequate contrast in a variety of workpiece images.
Furthermore, conventional vision systems can also adjust or select the circumferential position of the source of diffuse lighting about an optical axis. Typically, the position of the diffuse lighting source is adjustable or selectable in, for example, addressable sectors or quadrants. As such, the field of view of the camera can be illuminated by any combination of sectors and quadrants of such a circular lighting system. Additionally, the intensity level of the light source can be coordinated with the circumferential position of the light source to optimize the illumination of a workpiece edge.
For example, some conventional vision systems include an annular light system that emits rectangular or toroidal patterns. The light system is an annulus which is divided into four quadrants. Other conventional vision systems include a ring light having an annulus which is subdivided into eight or more sectors. Additionally, some conventional vision systems have hemispherically-shaped light systems to direct light from a multitude of positions relative to an optical axis. The center of the hemisphere serves as a focal point for the light sources. Furthermore, any combination of sectors or quadrants can simultaneously be illuminated with varying illumination levels.
In other conventional programmable ring lighting systems, a very large number of fiber optic cables are arranged such that first ends of the fiber optical cables receive light from a high-intensity light source, such as a halogen lamp. The second ends of the fiber optic cables are arranged in a ring around the optical axis. The fiber optic cables, or sets of the fiber optic cables, can be individually controlled to project the light from the light source onto the field of view of the camera using an annular mirror and a parabolic annular mirror.
Recently, manufacturers of conventional vision systems have started offering a solid-state replacement for the traditional halogen lamps that have been used in conventional diffuse light sources. These manufacturers now offer light emitting diodes (LEDs) that offer high reliability, a longer service life, lower cost, good intensity modulation capabilities and a wide variety of frequency ranges.
One exemplary solid-state lighting system is disclosed in U.S. Pat. No. 5,580,163 to Johnson, II. As shown in FIG. 13, the 163 patent discloses a focusing light source with a flexible mount 502 for multiple light-emitting elements 504. Each light-emitting element 504 emits a beam of light onto a work piece 506 at a predetermined azimuthal angle xcex1n to form a predetermined pattern of light. To adjust or focus the multiple light-emitting elements 504, the flexible mount 502 is rotated in one direction toward the center of the mount 502 or a second direction away from the center of the mount 502. In various other embodiments, the light-emitting elements 504 can be separately colored light-emitting elements. To achieve multi-colored illumination, illumination from a plurality of the light-emitting elements 504 is combined at the workpiece.
The total azimuthal angle range corresponding to the sources used to achieve a particular multi-colored illumination is approximately xxcex1n, where x is the number of different colored light-emitting elements 504 used. Thus, the multi-colored illumination provided by such a system cannot be controlled in azimuthal angle increments which are as narrow as the light emitting elements 504. Furthermore, any shadows in the field of view will exhibit zones of various colors, since each color component in the illumination is projected form a slightly different direction. Additionally, the illumination density, that is the illumination intensity projected onto the field of view on the workpiece from a given azimuthal angle range, is significantly limited by the characteristics of the individual conventional light-emitting elements 504.
Another exemplary lighting system is identified as prior art in the 163 patent itself. As a shown in FIG. 14 of the 163 patent, a beam of light is emitted from a light-emitting element 504 towards a work piece 506 at an angle of incidence xcex2 determined by the angle of the pivoting member 503. This exemplary lighting system generally suffers the previously discussed limitations of the lighting system of the 163 patent if solid-state sources are used for the light-emitting elements 504.
Furthermore, FIG. 14 illustrates another characteristic of conventional adjustable lighting systems. Conventional lighting systems emit a beam of approximately circular cross-section from each light-emitting element. The beams may also be collimated or focused. However, when a beam of light is emitted at an angle of incidence xcex21 which is not normal to the illuminated workpiece surface, an approximately oval-shaped or elliptical pattern is created on a planar work piece 506 with an illumination field 512 having edges at a given x1 and y1 distance from the center of the illumination field 512, where x1 is greater than y1.
Moreover, as the angle of incidence increases as shown by xcex22, when the beam intersects with a plane positioned along the optical axis 508 the distance y1 of the illumination field 514 is approximately the same as y1 of the illumination field 512, while the distance x2 of the illumination field 514 becomes longer than x1. Since the field of view along an optical system axis 508 is generally a circle centered about the optical axis, such elliptical illumination fields are not desirable for achieving the maximum illumination density for a given type of light-emitting element. For example, if the distance y1 is set approximately at the edge of a circular field of view, the distance x1 will extend beyond the edge of the field of view and a significant amount of available illumination energy will be wasted outside of the field of view.
Another exemplary solid-state lighting system is disclosed in U.S. Pat. No. 5,897,195 to Choate. The 195 patent discloses an oblique LED illuminator device with a cylindrical or truncated-conical array of LEDs. The array of LEDs produces collimated light beams that are directed onto axially-spaced, inclined surfaces formed on the outer periphery of a hollow, similarly-shaped Fresnel-like diffuser. The associated Fresnel-like diffuser refracts and directs rings of light beams onto the surface of a workpiece at variable angles of incidence. The array of LEDs coaxially surrounds the associated Fresnel-like diffuser. The associated Fresnel-like diffuser has annular, prism-shaped projections which differ in shape depending upon the desired angle of incidence. To create a beam of light with a desired angle of incidence, a light beam is emitted from an LED to the projection within the associated Fresnel-like diffuser, which redirects the light beam onto the workpiece at the desired angle of incidence. The lighting system of the 195 patent generally suffers the previously discussed limitations of the lighting system of the 163 patent when solid-state sources are used for the light-emitting elements.
Yet another exemplary solid-state lighting system is disclosed in U.S. Pat. No. 4,706,168 to Weisner, which is incorporated herein in its entirety. In the 168 patent, light from a ring source is directed toward a curved parabolic surface on a light collector ring. The curved parabolic surface substantially collimates the light and fans the light out radially toward a toroidal reflector surface on an encompassing ring. The relative angle of the light from the light source toward the parabolic surface and the position of the parabolic surface relative to the toroidal reflector surface determines the angle of incidence of a cone of light that falls in the region of the object, to illuminate particular features.
One exemplary method for combining light from a plurality of light sources is disclosed in U.S. Pat. No. 4,911,532 to Hidaka, which is incorporated herein by reference in its entirety. The 532 patent discloses a laser optical system with a single collimating lens and combining device. A collimating lens unit and a plurality of semiconductor lasers that emit laser beams of mutually different wavelengths are attached to the base of a light source unit. The laser beams are superposed one on top of another through dichroic prisms before impinging on the collimating lens. To superimpose the laser beams on top of each other, the optical axes and the diameters of the beams are adjusted by separate fine adjustment units.
An exemplary single dichroic prism is disclosed in U.S. Pat. No. 5,880,889 to Neumann et al., which is incorporated herein in its entirety. The 889 patent discloses a three-color dichroic beamsplitter/combiner usable to separate or combine unpolarized light. The beamsplitter/combiner separates a beam of light into three frequency bands corresponding to a first color, a second color, and a third color. The configuration of the glass support structure is chosen so that the first color of light is directed in a first direction, the second color of light is directed in a second direction, and the third color of light is directed in a third direction.
However, none of the 163, 195 and 168 patents disclose a lighting system for projecting a variable color along a single beam path when using a plurality of light sources. Furthermore, it should be appreciated that the optical energy available from relatively economical and compact solid state light emitting devices is relatively limited compared to conventional halogen light sources and fiber optic cable light sources. It should also be appreciated that none of the 163, 195 and 168 patents disclose techniques for combining a plurality of solid-state device light beams into a compound light-emitting element which provides a relatively high white-light illumination density along a relatively narrow azimuthal angle range in a lighting system. Furthermore, superimposing a plurality of laser beams with separate adjustment units can be especially difficult when the space for mounting the laser sources and their adjustment units is severely constrained. Superimposing the plurality of laser beams can also be difficult when using two dichroic prisms, as disclosed in the 532 patent.
This invention provides control systems and methods that enhance the diffuse lighting effects that are currently offered on the market.
This invention separately provides systems and methods that create conventional as well as more refined and versatile diffuse illumination using a simpler, more robust device.
This invention separately provides systems and methods that align a plurality of light beams from a set of two or more solid-state sources in a compact space.
This invention separately provides systems and methods that combine a plurality of light beams within a compound source.
This invention separately provides systems and methods that increase the illumination density available from a specific direction in an illumination field when using a combination of solid-state light sources.
This invention separately provides systems and methods that orient one or more solid-state light sources so that a beam of uneven optical energy distribution is oriented to provide a desirable illumination distribution in an illumination field.
This invention separately provides systems and methods that align the major axis of the cross-section of a shaped light beam relative to an optical path to provide a desirable illumination distribution in an illumination field.
This invention separately provides systems and methods such that the major axis of an illuminating light beam lies in a plane that is approximately normal to an optical axis of a system that receives images of objects illuminated by the light beam.
This invention separately provides systems and methods that align a plurality of light beams from a set of two or more of solid-state devices along a single beam path.
This invention separately provides systems and methods that create illumination containing a desired wavelength combination at a high level of spatial addressability.
In various exemplary embodiments, the control systems and methods of this invention include a light emitting source which emits a light beam containing at least one color of light, a lens that shapes the cross-section of the beam of light preferentially along at least one cross-section axis, and a reflective surface which reflects the beam of light along an angle of incidence. In other exemplary embodiments, the control systems and methods of this invention, further comprise a compound light emitting source comprising a plurality of light emitting devices with a prism that aligns the beams of light from the light-emitting devices along a single beam path toward the lens, where the plurality of light emitting devices include a green light emitting device, red light emitting device and blue light emitting device, thus creating a multiple wavelength light beam capable of supporting relatively high illumination densities.
Further, in other exemplary embodiments, the lens is a Fresnel lens which shapes the cross-section of the beam of light to create an elliptically-shaped cross-section with a major axis and a minor axis, where the major axis lies in a plane that is approximately normal to an optical axis of a system that receives images of objects illuminated by the light beam. Additionally, in other exemplary embodiments, the reflective surface comprises a first reflective surface and a second reflective surface. The beam of light is reflected perpendicularly by the first reflective surface onto a particular portion of the second reflective surface. The particular portion of the second reflective surface aligns the beam of light along the angle of incidence. The first reflective surface and second reflective surface are movable relative to each other to create the angle of incidence.
An exemplary embodiment of the systems and methods of this invention further incorporates the systems and methods for illuminating objects for vision systems as described in the 168 patent, and a three color dichroic beam combiner similar to the dichroic beamsplitter/combiner described in the 889 patent.
These and other objects of the invention will be described in or be apparent from the following description of the exemplary embodiments.